1. Field of the Invention
The present invention relates to a data structure and signaling method for an emergency alert message and a digital TV receiver, in which the emergency alert message is transmitted as an in-band signal from a digital cable broadcast transmitter.
2. Discussion of the Related Art
Generally, a cable set-top box is needed to receive digital cable broadcasts. The digital cable set-top box, which is connected to a cable headend (a sort of a broadcasting station) sending digital cable programs, receives an A/V broadcast program via in-band of a cable frequency band and data broadcasts via out-of-band (OOB). Specifically, the cable set-top box makes bi-directional communications with the headend via OOB.
There are broadcasting protocols such as SI (service information) and PSIP (program and system information protocol) for transmitting channel and broadcast programs guide information. To secure stability in cable broadcasting, the SI is transmitted via OOB (i.e., as an out-of-band signal) and the PSIP information is transmitted via in-band (i.e., as an in-band signal). And, as digital cable broadcast receivers, there are U.S. Open Cable, European DVB-C, Japanese ISDB-C and the like.
The open cable broadcast receiver is a system that separates a POD (point of deployment) module including a conditional access (CA) system from a body of a digital cable set-top box for the copy prevention and conditional access to valuable broadcast contents. Thus, the open cable broadcast receiver provides an easy replacement function of a security system and enables a retail sale, whereby low-price digital cable broadcast receivers can be supplied. The POD module uses a PCMCIA card to be loaded in a slot of the digital cable set-top box for instance. Hence, the POD module is occasionally called a cable card. And, the POD module and the cable card will be used without distinction in the following description.
Meanwhile, there is a cable-ready digital TV capable of receiving cable broadcasting without a cable set-top box to enable a retail sale that the open cable system pursues. Namely, the cable-ready digital TV has a built-in cable set-top box to receive terrestrial analog broadcasting, terrestrial digital broadcasting, cable analog broadcasting and cable digital broadcasting without a separate cable set-top box, thereby enabling a user to view all kinds of the broadcasts.
A receiver capable of receiving cable broadcasting, e.g., a cable-ready digital TV has a basic protocol of receiving to process an emergency alert message transmitted from a transmitting side to prepare for an emergency situation. Namely, the cable-ready digital TV receives an emergency alert message transmitted via a specific frequency of a terrestrial wave or cable, makes a channel change into a specific channel of the terrestrial wave or cable to effectively provide information of an emergency alert to a user currently watching the TV, and then outputs the information of the emergency alert. After the emergency alert situation has ended, the specific channel should be changed into the previous channel the user previously watched. Hence, such complicated situations are regulated as the basic protocol of the cable-ready digital TV.
The emergency alert message can be transmitted via OOB or in-band. The cable-ready digital TV receives the emergency alert message transmitted via OOB if the POD module is loaded or the emergency alert message transmitted via in-band if the POD module is not loaded. A specific channel of the emergency alert message transmitted via in-band corresponds to a two-part channel number consisting of a channel pair (e.g., 100-3) having a major channel number (i.e., physical channel number) and a minor channel number (i.e., a program number).
Meanwhile, an analog cable channel has no minor channel. In other words, the major channel number of an analog cable channel is the channel number of a particular physical channel and its minor channel number is set to a null value which represents a predetermined value (e.g., a value of 0) indicating that there is no minor channel. The channel numbering of an analog cable channel is similar to that of an analog terrestrial channel which has a minor channel number set to 0. In addition, when the minor channel number of a digital cable channel is set to a null value, its channel number simply becomes a one-part channel number including its major channel number only.
Therefore, if an emergency alert message is received via in-band since the POD module is not loaded, a minor channel number of a details channel included in the emergency alert message can have a null value.
Thus, the conventional emergency alert message signaling method is unable to clearly identify whether the details channel to be tuned is the analog channel or the digital channel represented by the one-part channel number in case that the minor channel number is set to a null value. So, the tuning to the details channel may be not performed properly.